Postpartum major depression (PPMD) is common, occurring in approximately 7% of women in the first three months after childbirth. PPMD can have a profound impact for the woman, decreasing quality of life, increasing emotional distress and reducing caregiving capacity, and can increase the risk of disturbances in infant development. A growing number of studies have shown that psychological treatments are effective at reducing the incidence of PPMD. In addition, women overwhelmingly prefer psychological treatment to medication while pregnant or breast feeding. However, numerous barriers exist that prevent women from accessing face-to-face services. The Internet offers great potential in extending preventive services to women in the perinatal period. While such interventions have not been investigated in this population, two broad classes of internet interventions have been evaluated. Individual Internet Interventions (IIIs), which provide patients with access to web-based self-management skills training programs, have been shown to be effective in reducing depression in general populations, particularly when accompanied by some human support via email or telephone coaching. Internet Support Groups (ISGs) appear to be commonly used by women in the perinatal period. However, randomized controlled trials have found them ineffective at reducing depression. Theories on the use of accountability to improve adherence and the application of online collaborative learning to enhance skill acquisition suggest that a careful integration of III and ISG could have a synergistic effect in improving both adherence and outcomes in online treatments to prevent depression. Thus, use of networked peers to enhance adherence and outcomes, instead of therapists or coaches, would make this intervention highly scalable. We have designed, constructed, and piloted a prototype of an online intervention, which we call Share that functionally integrates an III and an ISG targeting skills to manage mood and prevent depression. Shared goal setting and supportive monitoring by networked peers is designed to increase adherence to the program. Shared learning tools are designed to enhance learning through group learning processes. Based on promising results in a pilot, we are proposing an RCT to evaluate Share. Women in weeks 20-28 of their pregnancy will be randomized to receive either Share or an III that will serve as a minimal treatment control. Share has the potential to provide a novel paradigm for the prevention of depression, one that is accessible, highly scalable and cost-effective.